Hi Mandy!
Unfortunately, this is correct. When dining at Cinderella's Royal Table for dinner, you will get your picture taken with Cinderella in the lobby before your meal, but that is the extent of princess interaction. The Fairy Godmother will make an appearance during dinner to announce special celebrations like birthdays, anniversaries and engagements, but she doesn't mingle among the tables or sign autographs.
If you would like the opportunity to have different princesses visit your table during your meal, I would recommend canceling your dinner reservations and try for breakfast or lunch at the castle. Breakfast is an all you care to eat pre-plated meal with scrambled eggs, bacon, sausage and potatoes. There is also fresh fruit and pastries. Lunch is ordered from a set menu.
Another option for dining with the princesses is
Akershus Royal Banquet Hall which is located in the Norway pavilion at Epcot. Breakfast, lunch and dinner all feature princesses who visit your table. There is also a photo package included with this meal, usually this photo is taken with Belle.
Good luck with whatever you decide. I hope your girls have a wonderful time!